1. Field of the Invention
The present invntion relates to a process for finishing optical lenses including processing steps of smoothing and polishing the lens, which is suitable in particular for the production of ophthalmic lenses, as well as to an apparatus for effecting such process.
2. Description of the Prior Art
In the production of optical glass lenses, especially of ophthalmic glass lenses, it has generally been practiced to process in such a manner, that a casted lens is first roughly ground using an abrasive and then subjected to a smoothing and a polishing to attain a contemplated optical surface of the lens in a sufficient accuracy. In the process steps of smoothing and polishing performed both in a similar manner as in the lapping, the lens held on a lens holder is placed on a finishing tool or lapping plate and the processing of lens surface is carried out by effecting a relative sliding movement of the lens and the finishing tool while supplying a lapping compound onto the lens. By the smoothing, the surface roughness of the lens is reduced and, by the polishing, the lens is finished in a sufficient accuracy into a smooth contemplated optical surface.
On the other hand, there have been brought into practical use plastic lenses produced by injection molding or casting in a mold. The surface of these plastic lenses produced in such techniques exhibits a sufficient optical accuracy, so that a finishing as in the case of glass lens can in general be dispensed with. In the practice, a plurality of standard models of molded plastic lenses having different diopters are provided, among which the user can select one suitable to him. Also in some cases of special optical prescriptions, a lens of special optical parameters different from those of the standard ones may be required. For preparing such a special lens, a molded lens having a thickness somewhat larger than that of the finished lens is employed and processed by smoothing and polishing, as in the case of glass lens.
The construction is the same for both the apparatuses for the smoothing and for the polishing and both include a conduit means for feeding processing compound and an arrangement for performing relative sliding motion of the finishing tool and the lens. Various arrangements for realizing such a relative sliding motion have been known, such as for example, the so-called UDAGAWA-arrangement, in which a triangular motion of the lens is incorporated with a rotating motion of the finishing tool, and the so-called AO-arrangement, in which a circular movement of the lens is combined with a rotary motion of the finishing tool. The finishing tool consists generally of a dish-like body having thereon a pad fixed with adhasive. The material of the dish and the type of the pad can adequately be chosen depending on the degree of finishing etc.
In the prior art practice, it is necessary to employ different processing tools and different lapping compounds for the smoothing and for the polishing, since the contemplated degree of surface finish is different for the smoothing and for the polishing. Thus, for the smoothing, a pad or a diamond or ceramic tool and a lapping compound both designated specifically therefor should be used and, for the polishing also, specifically designed ones are necessary. For this reason, two processing machines for the smoothing and for the polishing have hitherto been employed, which has resulted in not only a forced expense for the investment costs for the installations but also laborious works for the trasference of the lens from the smoothing machine to the polishing machine together with works for mounting and dismounting of the lens after the smoothing. A further dificulty may accompany by the circumstances that it is difficult to maintain the processing conditions for the smoothing and for the polishing due to the unavoidable errors or discrepancies in the dimension and in the motion between the smoothing and the polishing, which will often bring about processing errors. This problem is quite significant in the production of optical lenses, in particular, ophthalmic lenses requiring high optical accuracy.